While that question might seem profound, it is basically a diversion tactic. I’ve seen it many times. I often see that atheists, when confronted with a particular argument for the existence of God, acts as if that is the only argument in existence, and often ignore what a particular argument tries to prove.
This argument doesn’t really prove the existence of God, or a deity, but proves that it can be reasonable to believe that God exists. This argument obviously needs to be combined with other arguments, like the cosmological argument, and with arguments surrounding Christ, and especially his resurrection.
The case for Christianity is the conclusion to many arguments or many pieces of data.
And as to his definition of faith, I would answer that it is impossible to lead a discussion when one of the participants uses an idiosyncratic definition of one of the key terms, a definition without any precedence.